An in vitro assay to detect association of nucleocapsids and viral-infected cell plasma membrane is being developed. Latex bead vesiculation is being employed to obtain plasma membranes from cells infected with vesicular stomatitis virus (VSV). The plasma membrane bound beads will be reacted with nucleocapsids and association will be monitored by discontinuous sucrose gradient centrifugation. The use of specific temperature-sensitive mutants of vesicular stomatitis virus should enable us to determine which of the viral membrane protein functions as the recognition site for nucleocapsids. In addition, the membrane bound latex beads offers an opportunity to investigate the spatial orientation of the VSV glycoprotein in the membranes of infected cells. Susceptibility to protease treatment as determined by a change in the mobility in polyacrylamide gels, and by tryptic peptide mapping will suggest that the VS viral glycoprotein spans the plasma membrane and is exposed on the inner surface of the membrane.